On Thu, Mar 22, 2018 at 01:10:22PM -0700, Joel Fernandes wrote: > On Wed, Mar 21, 2018 at 8:35 AM, Patrick Bellasi > <patrick.bell...@arm.com> wrote: > > [...] > > > >> @@ -6555,6 +6613,14 @@ select_task_rq_fair(struct task_struct *p, int > >> prev_cpu, int sd_flag, int wake_f > >> break; > >> } > >> > >> + /* > >> + * Energy-aware task placement is performed on the highest > >> + * non-overutilized domain spanning over cpu and prev_cpu. > >> + */ > >> + if (want_energy && !sd_overutilized(tmp) && > >> + cpumask_test_cpu(prev_cpu, sched_domain_span(tmp))) > >> + energy_sd = tmp; > >> + > > > > Not entirely sure, but I was trying to understand if we can avoid to > > modify the definition of want_affine (in the previous chunk) and move > > this block before the previous "if (want_affine..." (in mainline but > > not in this chunk), which will became an else, e.g. > > > > if (want_energy && !sd_overutilized(tmp) && > > // ... > > else if (want_energy && !sd_overutilized(tmp) && > > // ... > > > > Isn't that the same? > > > > Maybe there is a code path I'm missing... but otherwise it seems a > > more self contained modification of select_task_rq_fair... > > Just replying to this here Patrick instead of the other thread. > > I think this is the right place for the block from Quentin quoted > above because we want to search for the highest domain that is > !overutilized and look among those for the candidates. So from that > perspective, we can't move the block to the beginning and it seems to > be in the right place. My main concern on the other thread was > different, I was talking about the cases where sd_flag & tmp->flags > don't match. In that case, sd = NULL would trump EAS and I was > wondering if that's the right thing to do...
You mean if SD_BALANCE_WAKE isn't set on sched_domains? The current code seems to rely on that flag to be set to work correctly. Otherwise, the loop might bail out on !want_affine and we end up doing the find_energy_efficient_cpu() on the lowest level sched_domain even if there is higher level one which isn't over-utilized. However, SD_BALANCE_WAKE should be set if SD_ASYM_CPUCAPACITY is set so sd == NULL shouldn't be possible? This only holds as long as we only want EAS for asymmetric systems.
